1. Field of the Invention
The present invention relates to an image reading apparatus configured to read an image of an original, which includes a light source configured to irradiate the original with light, an optical system configured to condense and image a light beam from the light source reflected back from a surface of the original, and a substrate member having a photoelectric conversion unit arranged at an imaging position of the optical system. Further, the present invention relates to an image forming apparatus including the image reading apparatus.
2. Description of the Related Art
Conventionally, in an image reading apparatus, it has been necessary to adjust and fix a lens as an optical system and a sensor such as a charge coupled device (CCD) as a photoelectric conversion unit at highly accurate relative positions so as to read an image of an original with satisfactory image quality. The satisfactory image quality refers to quality of an image obtained at correct focus point and magnification with less chromatic aberration. Although the accuracy of positional adjustment depends on the type and size of a lens, accuracy on the order of micrometers is required in a case of a lens of a general reduction optical system. As a fixing method to be performed after the positional adjustment, there have conventionally been employed a fixing method with a screw or soldering, a bonding method with an adhesive or an ultraviolet (UV) curable resin, and the like.
The screw fixing is advantageous in that the fixing and releasing are easy, but is less accurate because of the disadvantage in that, due to the characteristics of the screw fixing method, the member is fixed by a given pressing force or greater and hence the fixed member may be deformed and moved along with the screw fastening. The soldering also provides easiness in the fixing and releasing, but the shrinkage amount at the time when solder is cooled and solidified is as large as several tens of micrometers, and the shrinkage amount changes depending on the amount of solder. Thus, accurate and stable fixing is difficult.
The adhesive other than the UV curable resin is disadvantageous in that it is difficult to unfix the member, but is advantageous in that the shrinkage amount at the time of curing is small. However, some adhesives require several hours or longer to be completely cured, or generate gas which fogs the lens or the like, and hence those adhesives need to be handled carefully. There is an instant adhesive which is cured within a short period of time, but this type of adhesive is cured through contact with moisture in the air, which leads to a drawback in that the curing time varies slightly.
Similarly to general adhesives, the UV bonding has difficulty in unfixing the member, and further, the member to be bonded and the like need to be transparent in many cases so as to securely irradiate the adhesive with UV light, which leads to a drawback in that the material to be used is limited. However, the shrinkage amount at the time of curing is as small as about 1% to 5% relative to the volume, and this shrinkage amount is equal to or smaller than that of the other types of adhesive. Thus, the UV bonding is an optimum method to ensure the fixing position on the order of micrometers. The curing time is several tens of seconds required during UV light irradiation, and the curing shrinkage amount is small as well. Thus, the UV bonding is convenient. Further, the UV bonding has a significant advantage in that the curing shrinkage amount and the curing time can be controlled appropriately by adjusting the UV light irradiation period and the adhesive application amount. The use of the UV bonding method is an optimum measure to positionally adjust and fix the optical system and the photoelectric conversion unit of the image reading apparatus on the order of micrometers.
As the inventions of fixation of the UV bonding method, the inventions of Japanese Patent No. 4,202,988 and Japanese Patent No. 4,113,320 are disclosed. The invention of Japanese Patent No. 4,202,988 relates to an image reading apparatus in which a holding member (support member) configured to hold a lens and a substrate member having a photoelectric conversion unit are coupled to each other through an intermediate holding member. The invention of Japanese Patent No. 4,113,320 relates to an image reading apparatus in which a housing (support member) configured to hold a lens and a substrate member having a photoelectric conversion unit are coupled to each other through an intermediate holding member.
However, in Japanese Patent No. 4,202,988 and Japanese Patent No. 4,113,320, the intermediate member is additionally required to couple the substrate member and the support member to each other.
Further, when the intermediate member is bonded with a photocurable adhesive, the intermediate member needs to be transparent so that the choice of materials is limited.
Still further, when joining the substrate member and the support member to each other, the substrate member and the support member are coupled to each other with an adhesive in a state in which the substrate member and the support member are in contact with the intermediate member, and hence, in the stage of positional adjustment between the substrate member and the support member, the movement of the substrate member and the support member is restricted so that the positional adjustment cannot be performed freely.